Multi-Level Collector Bipolar Transistor Design
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Solution Overview
Problem
Existing semiconductor technologies face challenges in simultaneously achieving high gain, high Early Voltage, and high breakdown voltage in bipolar transistors, particularly in large-scale production where manufacturing optimization and cost considerations limit doping profile variations.
Innovation Solution
The implementation of a multi-level collector structure combined with a lightly doped base region in bipolar transistors, where the multi-level collector structure includes a deep collector tip, a shallower central collector, and a self-aligned intermediate portion, allowing for high current gain, high Early Voltage, and preserved breakdown voltages using commonly available doping profiles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If doping profiles are adjusted to achieve high gain, then manufacturing complexity and cost increase
Solution Approach 1:
The collector region is segmented into multiple levels with different doping concentrations and depths. The first collector region has a first doping concentration, the second collector region has a second doping concentration, and the third collector region has a third doping concentration. This segmentation allows each region to contribute differently to transistor performance, achieving high gain through optimized doping profiles without requiring complex manufacturing variations across the entire device.
Solution Approach 2:
Different regions of the collector are assigned different local properties through varying doping concentrations. The first collector region near the base-emitter junction has one doping concentration optimized for gain, while the second and third collector regions have different doping concentrations optimized for breakdown voltage and Early Voltage. This local quality approach resolves the contradiction by allowing high gain in specific regions without compromising overall manufacturing simplicity.
2Reliability
If doping profiles are varied to achieve high Early Voltage, then manufacturing optimization and cost considerations are compromised
Solution Approach 1:
The collector is divided into segmented regions with progressively different doping concentrations. The first collector region has a first doping concentration, the second collector region has a second doping concentration, and the third collector region has a third doping concentration. This segmentation enables high Early Voltage through optimized electric field distribution in each region while maintaining compatibility with standard manufacturing processes that can handle multiple doping levels.
Solution Approach 2:
The invention introduces a vertical dimension to doping concentration variation by creating multiple collector regions at different depths below the semiconductor substrate. The first collector region is at a first depth, the second collector region is at a second depth, and the third collector region is at a third depth. This vertical dimensionality allows optimization of Early Voltage through depth-dependent doping profiles without complicating lateral manufacturing processes.
3Reliability
If conventional single-level collector structure is used, then breakdown voltage is limited
Solution Approach 1:
The collector region is segmented into three distinct levels: first collector region, second collector region, and third collector region, each with different doping concentrations and depths. This segmentation creates a progressive doping profile that extends the breakdown voltage capability by distributing the electric field stress across multiple regions with optimized local properties, rather than relying on a single uniform collector structure.
Solution Approach 2:
The collector structure functions as a composite semiconductor structure with multiple regions having different doping concentrations. The first collector region, second collector region, and third collector region form a composite structure where each region contributes different electrical properties, analogous to composite materials in other fields. This composite approach achieves high breakdown voltage by combining regions with optimized characteristics rather than using a homogeneous structure.
Data Source
AI summary
Bipolar transistors and methods for fabricating bipolar transistors are provided. In one embodiment, the method includes the step or process of providing a substrate having therein a semiconductor base region of a first conductivity type and first doping density proximate an upper substrate surface. A multilevel collector structure of a second opposite conductivity type is formed in the base region. The multilevel collector includes a first collector part extending to a collector contact, a second collector part Ohmically coupled to the first collector part underlying the upper substrate surface by a first depth, a third collector part laterally spaced apart from the second collector part and underlying the upper substrate surface by a second depth and having a first vertical thickness, and a fourth collector part Ohmically coupling the second and third collector parts and having a second vertical thickness different than the first vertical thickness.